Working with C# Anonymous Types

Answer 1

You cannot do this with anonymous types. Just create a Contact class/struct and use that.

List<object> list = new List<object>();
foreach ( Contact c in allContacts ) {
    list.Add( c );
}

Then you can do this:

foreach ( var o in list ) {
    Console.WriteLine( o.ContactID );
}

...or this:

foreach ( object o in list ) {
    Console.WriteLine( ((Contact)o).ContactID ); //Gives intellisense
}

Of course you should in that case just do create a Contact list instead of an object list:

List<Contact> list = new List<Contact>();
foreach ( Contact c in allContacts ) {
    list.Add( c );
}

EDIT: Missed essential part of the question. Now fixed.
EDIT: Changed answer yet again. See above.

Answer 2

i would use

allContacts
 .Select(c => new { c.ContactID, c.FullName })
 .ToList()
 .ForEach(c => {
   ...do stuff;
 });

then you dont need to declare at all. i believe that less declaration, less semi-colon leads to less bug

Answer 3

foreach ( var o in list ) {
    Console.WriteLine( o.ContactID );
}

this will work only if list is IEnumerable<anonymous type>, like this:

var list = allContacts.Select(c => new {
        ContactID = c.ContactID,
        FullName = c.FullName
    });
}

but you can't return anonymous types, because you must define return type (you can't return var) and anonymous types can't have names. you should create non-anonymous type if you with to pass it. Actually anonymous types should not be used too much, except for inside of queries.

Answer 4

replacing object with var in for each construct may work

Answer 5

list back

public static void Main()
{
    foreach (object item in GetList())
    {
        var x = Cast(item, new { ContactID = 0, FullName = "" });
        Console.WriteLine(x.ContactID + " " + x.FullName);
    }

}

public static IEnumerable<object> GetList()
{
    yield return new { ContactID = 4, FullName = "Jack Smith" };
    yield return new { ContactID = 5, FullName = "John Doe" };
}

public static T Cast<T>(object obj, T type)
{
    return (T)obj;
}

Answer 6

You can't return a list of an anonymous type, it will have to be a list of object. Thus you will lose the type information.

Option 1
Don't use an anonymous type. If you are trying to use an anonymous type in more than one method, then create a real class.

Option 2
Don't downcast your anonymous type to object. (must be in one method)

var list = allContacts
             .Select(c => new { c.ContactID, c.FullName })
             .ToList();

foreach (var o in list) {
    Console.WriteLine(o.ContactID);
}

Option 3
Use the dynamic keyword. (.NET 4 required)

foreach (dynamic o in list) {
    Console.WriteLine(o.ContactID);
}

Option 4
Use some dirty reflection.